Waveguide with 2-layer stack-up

ABSTRACT

A lightweight stacked optical waveguide using two plastic substrates having nano-structure gratings and a single glass substrate sandwiched between them. The nano-structure gratings face each other, and are each encapsulated within the optical waveguide. The two plastic substrates are each adhesively secured to the central glass substrate rather than to each other to provide sufficient securing strength and precisely establish and maintain an air gap between the substrates. The thickness of the plastic substrates and the glass substrate are selected such that the stacked optical waveguide is lightweight, but also has sufficient drop performance. The stacked optical waveguide can be efficiently manufactured as the adhesive bonds a plastic substrate to a glass substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 63/076,583, filed on Sep. 10, 2020, the contents of which areincorporated fully herein by reference.

TECHNICAL FIELD

The present subject matter relates to optical waveguides used in adisplay, such as for an eyewear device including smart glasses andheadwear.

BACKGROUND

Optical waveguides may be formed using techniques which may createdefects.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures depict one or more implementations, by way ofexample only, not by way of limitations. In the figures, like referencenumerals refer to the same or similar elements.

FIG. 1 illustrates a stacked optical waveguide having two glasssubstrates secured to each other;

FIG. 2 illustrates a stacked optical waveguide having two plasticsubstrates each secured to one glass substrate sandwiched between theplastic substrates; and

FIG. 3 illustrates a flow diagram of a method of making the stackedoptical waveguide.

DETAILED DESCRIPTION

This disclosure includes examples of a lightweight stacked opticalwaveguide using two plastic substrates having nano-structure gratingsand a single glass substrate sandwiched between them. The nano-structuregratings face each other, and are each encapsulated within the opticalwaveguide. The two plastic substrates are each adhesively secured to thecentral glass substrate rather than to each other to provide sufficientsecuring strength and precisely establish and maintain an air gapbetween the substrates. The thickness of the plastic substrates and theglass substrate are selected such that the stacked optical waveguide islightweight, but also has sufficient drop performance. The stackedoptical waveguide can be efficiently manufactured as the adhesive bondsa plastic substrate to a glass substrate.

Additional objects, advantages and novel features of the examples willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing and the accompanying drawings or may be learned by productionor operation of the examples. The objects and advantages of the presentsubject matter may be realized and attained by means of themethodologies, instrumentalities and combinations particularly pointedout in the appended claims.

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant teachings. However, it should be apparent to those skilledin the art that the present teachings may be practiced without suchdetails. In other instances, well known methods, procedures, components,and circuitry have been described at a relatively high-level, withoutdetail, in order to avoid unnecessarily obscuring aspects of the presentteachings.

The term “coupled” as used herein refers to any logical, optical,physical or electrical connection, link or the like by which signals orlight produced or supplied by one system element are imparted to anothercoupled element. Unless described otherwise, coupled elements or devicesare not necessarily directly connected to one another and may beseparated by intermediate components, elements or communication mediathat may modify, manipulate or carry the light or signals.

The orientations of the eyewear device, associated components and anycomplete devices incorporating an eye scanner and camera such as shownin any of the drawings, are given by way of example only, forillustration and discussion purposes. In operation for a particularvariable optical processing application, the eyewear device may beoriented in any other direction suitable to the particular applicationof the eyewear device, for example up, down, sideways, or any otherorientation. Also, to the extent used herein, any directional term, suchas front, rear, inwards, outwards, towards, left, right, lateral,longitudinal, up, down, upper, lower, top, bottom and side, are used byway of example only, and are not limiting as to direction or orientationof any optic or component of an optic constructed as otherwise describedherein.

Reference now is made in detail to the examples illustrated in theaccompanying drawings and discussed below.

Referring to FIG. 1, a stacked optical waveguide 10 may use two glasssubstrates 12 and 14 with a single cover substrate 16. The stackedoptical waveguide 10 is suitable as an image display, such as asee-through display for eyewear including smart glasses and headgear.Each of the optically transparent glass substrates 12 and 14, and cover16 are spaced from each other by an adhesive 18 at their edges to createair gaps 20 and 22 to achieve the necessary optical stack-up, andencapsulate optical nano-structure gratings 24 for reliability purposes.Plastic substrates are desirable from a product weight and dropperformance perspective. However, mimicking the glass substratewaveguide stack 10 exactly with plastic substrates introduces laminationchallenges between two plastic substrates, i.e. laminating two “soft”substrates together, with an air gap while maintaining a constant gapbetween them.

Referring to FIG. 2, this disclosure provides an improved stackedoptical waveguide 30 to achieve a waveguide stack using two plasticsubstrates 32 and 34 and a single “hard” glass cover 36 therebyproviding benefits on product weight and reliability. The plasticsubstrates 32 and 34 are each lighter in weight than the glass substrate36 to provide a lighter stacked optical waveguide 30. Each of theplastic substrates 32 and 34 are adhered to opposite sides of the glasscover 36 sandwiched between them by adhesive 38 at their edges with airgaps 40 and 42 formed between them, as shown. Each of the plasticsubstrates 32 and 34 are optically transparent and have respectiveoptical nano-structure gratings 44 facing the glass cover 36 and eachother. This removes the challenges of adhering two soft plasticsubstrates 32 and 34 to each other, which poses challenges in terms ofmaintaining a constant air gap between them needed for acceptablewaveguide performance having an acceptable modulation transfer function(MTF). The soft plastic substrates 32 and 34 are each secured to thehard glass substrate 36 on either side which can be supported inmanufacturing. This design provides a “constant thickness” glasssubstrate 36 as the physical spacer and backbone between the two plasticsubstrates dominating the spacing, as opposed to stacking the two softsubstrates 32 and 34 against each other which are subject to “flop”which may result in a changing gap between the layers.

In addition, this disclosure allows the glass substrate 36 to bedecoupled from the waveguide functionality itself, as the glasssubstrate 36 does not include the optical nano-structure gratings 24.This allows using conventional chemically strengthened glass for glasssubstrate 36 (Gorilla® glass as an example). This in turn enables usingthinner glass for glass substrate 36, helping reduce product weightwhile maintaining product drop performance via use of the chemicallystrengthened glass.

The chemically strengthened glass substrate 36 further helps productperformance from a drop perspective, which is a distance a device can bedropped and functionally survive the impact of the fall, as typicalwaveguide glass substrates are not chemically strengthened which poses arisk from a product drop perspective. Also, having each of the waveguidestructures 32 and 34 facing the glass substrate 36 and sealed byadhesive 38 enables excellent reliability performance as well, as thenano-structure gratings 44 are encapsulated in this stack and notexposed to the environment.

In one example, the thickness of the glass substrate 36 may be between300 and 1000 microns, and each of plastic substrates may have athickness between 50-1000 microns. The thickness of the adhesive 38 mayhave a thickness between 50-100 microns and thus the spacing of the airgaps 40 and 42 may between 50-100 microns. However, limitation to thesethicknesses is not to be inferred. These dimensions are established toprovide good drop performance while limiting the weight of the stackedoptical waveguide 30.

Referring to FIG. 3, there is shown a flowchart of a method 300 offorming the stacked optical waveguide 30.

At block 302, the respective plastic substrates 32 and 34 are formedusing conventional processing techniques. The respective nano-structuregratings 44 provide waveguides for light to pass therethrough and forman image display. The glass substrate 36 is also formed, and may bechemically strengthened glass, which further helps product performancefrom a drop perspective.

At block 304, the plastic substrate 32 is secured to the glass substrate36 with adhesive 38 at the edges of the substrates. The plasticsubstrate 32 is oriented such that the respective nano-structuregratings 44 face the glass substrate 36. The adhesive establishes athickness of the respective gap 38.

At block 306, the plastic substrate 34 is secured to the glass substrate36 with adhesive 38 at the edges of the substrates. The plasticsubstrate 34 is also oriented such that the respective nano-structuregratings 44 face the glass substrate 36. The adhesive establishes athickness of the respective gap 38.

It will be understood that the terms and expressions used herein havethe ordinary meaning as is accorded to such terms and expressions withrespect to their corresponding respective areas of inquiry and studyexcept where specific meanings have otherwise been set forth herein.Relational terms such as first and second and the like may be usedsolely to distinguish one entity or action from another withoutnecessarily requiring or implying any actual such relationship or orderbetween such entities or actions. The terms “comprises,” “comprising,”“includes,” “including,” or any other variation thereof, are intended tocover a non-exclusive inclusion, such that a process, method, article,or apparatus that comprises or includes a list of elements or steps doesnot include only those elements or steps but may include other elementsor steps not expressly listed or inherent to such process, method,article, or apparatus. An element preceded by “a” or “an” does not,without further constraints, preclude the existence of additionalidentical elements in the process, method, article, or apparatus thatcomprises the element.

Unless otherwise stated, any and all measurements, values, ratings,positions, magnitudes, sizes, and other specifications that are setforth in this specification, including in the claims that follow, areapproximate, not exact. Such amounts are intended to have a reasonablerange that is consistent with the functions to which they relate andwith what is customary in the art to which they pertain. For example,unless expressly stated otherwise, a parameter value or the like mayvary by as much as ±10% from the stated amount.

In addition, in the foregoing Detailed Description, it can be seen thatvarious features are grouped together in various examples for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimed examplesrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, the subject matter to be protected liesin less than all features of any single disclosed example. Thus, thefollowing claims are hereby incorporated into the Detailed Description,with each claim standing on its own as a separately claimed subjectmatter.

While the foregoing has described what are considered to be the bestmode and other examples, it is understood that various modifications maybe made therein and that the subject matter disclosed herein may beimplemented in various forms and examples, and that they may be appliedin numerous applications, only some of which have been described herein.It is intended by the following claims to claim any and allmodifications and variations that fall within the true scope of thepresent concepts.

What is claimed is:
 1. A stacked optical waveguide, comprising: a glasssubstrate; a first plastic substrate having a first optical structure,the first plastic substrate secured to and spaced from the glasssubstrate; and a second plastic substrate having a second opticalstructure, the second plastic substrate secured to and spaced from theglass substrate such that the glass substrate is interposed between theplastic substrates.
 2. The waveguide as specified in claim 1, whereinthe optical structures comprise optical gratings.
 3. The waveguide asspecified in claim 2, wherein the optical structures face one another.4. The waveguide as specified in claim 1, wherein the plastic substratesare each secured to the glass substrate using an adhesive.
 5. Thewaveguide as specified in claim 1, wherein the plastic substrates andthe glass substrate are each optically transparent.
 6. The waveguide asspecified in claim 1, further comprising an air gap between the plasticsubstrates and the glass substrate.
 7. The waveguide as specified inclaim 1, wherein the plastic substrates are softer than the glasssubstrate.
 8. The waveguide as specified in claim 1, wherein the plasticsubstrates are each lighter than the glass substrate.
 9. The waveguideas specified in claim 1, wherein the glass substrate is chemicallyhardened.
 10. The waveguide as specified in claim 9, wherein the glasssubstrate has a thickness of between 50 and 100 microns.
 11. A method ofprocessing a stacked optical waveguide, comprising: securing a firstplastic substrate to a glass substrate, the first plastic substratehaving a first optical structure, the first plastic substrate spacedfrom the glass substrate; and securing a second plastic substrate to theglass substrate, the second plastic substrate having a second opticalstructure, the second plastic substrate spaced from the glass substratesuch that the glass substrate is interposed between the plasticsubstrates.
 12. The method as specified in claim 11, wherein the opticalstructures comprise optical gratings.
 13. The method as specified inclaim 12, wherein the optical structures face one another.
 14. Themethod as specified in claim 11, wherein the securing comprises securingthe plastic substrates to the glass substrate using an adhesive.
 15. Themethod as specified in claim 11, wherein the plastic substrates and theglass substrate are each optically transparent.
 16. The method asspecified in claim 11, further comprising generating an air gap betweenthe plastic substrates and the glass substrate.
 17. The method asspecified in claim 11, wherein the plastic substrates are softer thanthe glass substrate.
 18. The method as specified in claim 11, whereinthe plastic substrates are each lighter than the glass substrate. 19.The method as specified in claim 11, wherein the glass substrate ischemically hardened.
 20. The method as specified in claim 19, whereinthe glass substrate has a thickness of between 50 and 100 microns.